The present invention relates to a liquid/gas separator for positioning in the lower part of a well intended for the production of fluids, such as hydrocarbons. The separator prevents the entry of gas into the production tubing string, but allows the entry of fluid in liquid form. The invention also relates to a method for improving the primary, secondary or tertiary recovery of reservoir hydrocarbons and to improved systems involving downhole liquid/gas separators for various hydrocarbon recovery applications.
Hydrocarbon recovery operations commonly allow reservoir gas within the formation to flow into the wellbore and to the surface with the liquid hydrocarbons. This practice initially drives high volumes of hydrocarbons into the well and up through the production tubing. Conventional hydrocarbon producing methods thus allow, and in many cases rely upon, the pressurized reservoir gases to directly assist in lifting the production fluids to the surface. This practice thus utilizes the pressure and liquid-driving capabilities of the reservoir gas to improve early well production recovery. While prevalent, this practice significantly reduces the ultimate recovery of liquid hydrocarbon reserves from the formation.
Liquid/gas separators have been used downhole in producing oil and gas wells to allow the entry of reservoir fluids which are in the liquid state into the tubular string that conveys the liquid fluids to the surface, and to prevent the entry of fluids in the gaseous state into the producing tubular string. One type of separation device, which remains immersed in the surrounding downhole fluid, includes a float and a valve arrangement. When this separation device is full of liquid, an open conduit is provided from the reservoir to the producing tubular. When the liquid is displaced by gas in the separation device, the float rises due to its increased buoyancy and a valve closes to prevent the entry of fluids into the producing tubular.
This separator thus includes a float activated valving system which opens when the separator is full of liquid and closes when that liquid is displaced by gas. The flotation system within this separator is configured to operate in the vertical or substantially vertical orientation. When the liquid/gas separator is open, the separator allows liquid to be transmitted by pressure energy within the producing formation upward through the tubular string which is positioned above a standing or check valve, and then to be lifted to the surface by a conventional pump powered by a reciprocating or rotating (progressive cavity) rod string. Other types of available downhole pumps, such as electrical submersible pumps or hydraulic (jet-type) pumps, may also be used to lift the liquid to the surface once it is entrapped above the liquid gas separator and within the production tubing string.
In practice, the downhole separator does little to cause or accelerate the separation of liquid and gas. Rather, the device senses the presence of a gas or a liquid within the device by the float, and allows only liquid entry into the production tubing string. The separator thus operates within a downhole well in a manner similar to a float operated valve controller which detects the liquid/gas interface within a surface vessel. One type of separation device marketed as the Korkele downhole separator has proven effective in many installations.
The separator may be placed and operated within a cased wellbore with a conventional diameter casing therein or may also be operated in an open hole. In either case, the separator may be suspended in the well from production tubing. The basic advantage of the Korkele downhole separator is that it improves performance of the well and the well-reservoir production system by allowing for the production of liquids only, i.e., it prevents the entry of gas from the reservoir into the production tubular string. The downhole separator as discussed above is more fully described in a July 1972 article in World Oil, pages 37-42. Further details with respect to this separator are disclosed in U.S. Pat. No. 3,643,740 granted to Kork E. Kelley and hereby incorporated by reference.
Other prior art includes U.S. Pat. Nos. 1,507,454 and 1,757,267. The ""454 patent discloses an automatic pump control system with an upright stem connected to a diaphragm to operate a standing valve. The ""267 patent discloses a gas/oil separator having a separating chamber located within the tubing and a mechanism for diverting the path of oil over an enlarged contact surface to separate free oil from gas.
U.S. Patents naming Kork Kelly as an inventor or co-inventor include U.S. Pat. Nos. 2,291,902; 3,410,217; 3,324,803; 3,363,581; and 3,451,477. The ""902 patent discloses a gas anchor having a float connected to a valve stem which operates a valve head. The ""217 patent discloses a separator for liquid control in gas wells. The ""803 patent discloses a device having a floating bucket connected by a rod for liquid/gas wells. A valve member is disclosed below and in close proximity to a check ball. The ""581 patent discloses a pressure balanced and full-opening gas lift valve. The ""477 patent relates to an improved method for effecting gas control in oil wells. The device includes a flotation bucket with an open top and a valve string including a valve member connected to the top of a rod, with the bottom of the rod connected to the bottom bucket. The ""740 patent discloses both methods and apparatus for effecting gas control in oil wells utilizing a flotation bucket with an open top and a valve string including a valve member connected to the top of a rod. U.S. Pat. No. 3,971,213 discloses an improved pneumatic beam pumping unit.
U.S. Pat. No. 3,408,949 discloses a bottom hole gas/liquid separator having a float tube encircling the lower end of a production tubing and adapted to move vertically within a housing. A production valve is disposed on the upper end of a spacer bar such that the float tube and spacer bar form a sand trap. U.S. Pat. No. 3,483,827 discloses a well producing device which utilizes a gas separator in a tubing string to separate liquid from gas prior to entry into a downhole pump. U.S. Pat. No. 3,724,486 discloses a liquid and gas separation device for a downhole well wherein a valve member is moveable and resiliently mounted on a moveable liquid container designed so that liquid will accumulate within the bore hole above the position where gas enters to decrease or prohibit the entry of gas into the bore hole. U.S. Pat. No. 3,993,129 discloses a fluid injection valve for use in well tubing for controlling the flow of fluid between the outside of the production tubing and the inside of the tubing.
More recently issued patents include U.S. Pat. Nos. 4,474,234 and 4,570,718. The ""234 patent discloses a hydrocarbon production well having a safety valve removably mounted in the production tubing beneath a pump. The ""718 patent relates to an oil level sensor system and method for operating an oil well whereby upper and lower oil well sensors control pumping of the well. U.S. Pat. No. 5,456,318 discloses a fluid pumping device having a fluid inlet valve disposed at its lower end for fluid flow into the body of the device, a plunger assembly disposed in the interior of the body for reciprocating movement, a seal which cooperates with the plunger assembly to divide the body into isolated upper and lower chambers and to divide the body from the production tube, and fluid flow control valves.
U.S. Pat. No. 5,653,286 discloses a downhole gas separator connected to the lower end of a tubing string designed such that primary liquid fluid flows into a chamber within the separator. U.S. Pat. No. 5,655,604 discloses a downhole production pump and circulating system which utilizes valves wherein the valve balls are attached to projector stems. U.S. Pat. No. 5,664,628 discloses an improved filter medium for use in subterranean wells.
None of the prior art discussed above fully benefits from the capability of an effective downhole liquid/gas separator. Further improvements are required to obtain the significant advantages realized by retaining within the downhole producing formation the inherent energy, i.e. the compressed gas, which drives the desired hydrocarbon products from the reservoir rock and into the wellbore so that they may be more efficiently produced. By preventing the formation gas at bottom of the well from entering the production tubing string and permitting only the entry of liquids into the tubing string, the retained potential energy and expansive properties of the gas may be effectively utilized to produce a higher percentage of liquid reserves than would otherwise be recovered by conventional technology. Alternatively, improved procedures for pumping liquid accumulations off gas wells are necessary to improve the performance of gas wells. Moreover, further improvements in a separation device, in methods of using a separation device, and in the configuration and operation of the overall hydrocarbon recovery system in which a separation device is employed are required to benefit from the numerous applications in which such a device may be effectively used to enhance recovery of hydrocarbons.
The disadvantages of the prior art are overcome by the present invention. An improved separation device, a method of operating a separation device, an improved overall hydrocarbon recovery system, and improved techniques for recovering hydrocarbons are hereinafter disclosed.
The present invention discloses an improved downhole liquid injector and improved techniques utilizing an injector for recovering hydrocarbons from producing reservoirs. Several basic concepts influence the benefits of utilizing the liquid injector of the present invention in various existing and planned well and/or reservoir producing systems. First, positive prevention of gas into the producing tubular improves the efficiency of an artificial lift pumping system by allowing the lift system to handle primarily liquids rather than a combination of liquids and gases. By providing for the positive prevention of gas into the production tubing, the artificial lift pumping system is efficiently pumping only primarily liquids. Conventional artificial lift systems which utilize a rod string to power a downhole pump thus operate more efficiently with liquid only flowing through the production tubing string. Preventing gas lock in downhole positive displacement and electrical submersible pumps is a major problem for the oil well operator with existing technology. Since the injector of the present invention substantially reduces or eliminates unwanted gas to the production tubing string, gas lock is avoided and the life and efficiency of positive displacement and submersible pumps is increased.
By preventing gas entry downhole into the production tubing string, the present invention also reduces the possibility of gas blowout through the surface production system. The present invention also reduces sucker rod stuffing box drying and wear to reduce leakage of fluids from the wellhead and minimize environmental problems associated with producing hydrocarbons.
The system of the present invention may significantly benefit from the concept of preventing gas production from the reservoir and thereby retaining the gas within the reservoir where it will continue to supply energy in the form of pressure to drive well fluids into the producing wellbore. By permitting only the inflow of reservoir liquids into the production tubing string and maintaining gases on the top of a liquid column in the well, a high percentage of natural gas remains in the reservoir where it provides the pressure to drive liquids toward the wellbore and creates a more efficient drainage mechanism to best utilize the principles of gravity separation.
By keeping gas within the reservoir, the present invention also creates a more effective liquid drainage pattern within the reservoir by reducing gas coning around the well and improving the maintenance of an effective gas cap drive to develop an enhanced liquid gravity drainage system. The system of the present invention thus acts to oppose the release of gas from the formation into the wellbore and minimize undesirable coning of a gas cap, while also promoting the generation and maintenance of a more effective gas cap drive.
By retaining the gas in the reservoir, the flow of desired liquid hydrocarbons into the wellbore is also assisted by retaining gas in solution within the crude oil to maintain a lower fluid viscosity, thereby lowering the resistance to flow of the crude oil through the reservoir. Since reservoir rock has a lower relative permeability to liquids than to gas, particularly when the crude loses its lighter components and becomes heavy, minimizing gas inflow and maintaining reservoir pressure keeps the crude more gas saturated and less viscous so that it is mobile and may more freely flow toward the wellbore area.
The injector of the present invention may also be used to significantly improve the efficiency of a downhole system designed to remove liquids, typically water, from the wellbore which impede the production of natural gas from a gas reservoir. By providing for the efficient removal of problem liquids which impede the production of gases from primarily gas reserve reservoirs, the efficiency of a gas recovery system may be significantly enhanced. Systems with a positive downhole gas shutoff for removing liquid accumulations will also be safer to operate since gas flow to the surface through the tubing string may be automatically and positively controlled if surface control is lost.
The techniques of the present invention may be used to improve long-term productivity and increase the recovery of hydrocarbon reserves from many existing oilfields. In new oilfields, particularly those in which it is desirable to prevent or limit the wasteful production or uneconomical recovery of natural gas which lowers ultimate crude recovery, the present invention offers a valuable completion option. Such new fields are continually being discovered and developed in isolated offshore locations, and in many countries which are just now developing their petroleum reserves.
The downhole separation device of the present invention, which is more properly termed a liquid injector, is a float-operated device that permits producing reservoir fluids to flow into a production tubing string but positively shuts off the entry of gas. In a preferred embodiment, the injector prevents entry of fine-grain sand into the interior of the injector tool by utilizing an improved screening device to provide significantly increased protection from sand entry and minimize filling and plugging by the fine-grained sand particles. The sand particle sizes excluded by the screening device do not significantly impede fluid flow. The screening device also provides advantages relating to the breakup of foams in the wellbore to enhance the flow of liquid rather than gas into the interior of the injector. In one embodiment of the injector, the flow shutoff valve is located at a high position within or above the intake tube and close to the standing or check valve. This positioning of the shutoff valve causes liquids in the intake tube to remain under wellbore pressure while the shutoff valve is closed, thus preventing the release of solution gas in response to pressure reduction caused by the pumping action, thus reducing problems associated with pump gas lock. Raising the shutoff valve also keeps the shutoff valve out of the lower area of the float in which sand may settle during the time the valve is closed, thus further minimizing the possibility of sand plugging.
An improved method is provided for creating a liquid reservoir within a well pumping or producing system. According to one technique, liquid does not flow directly into the pump intake, and instead the wellbore formation fluid is first diverted into a vertical reservoir created in an annulus between the tubing and the casing by addition of a packer. The downhole pump may then draw from this reservoir. Should the injector shutoff valve close, the pump would continue to draw liquid until the working fluid level drops to the pump intake. An additional benefit from this concept occurs as a result of further solution gas breakout and separation within the vertical reservoir. The gas from the producing formation below the packer may be vented through a vent tube containing a pressure regulation system to ensure wellbore pressure sufficient to lift liquid to a working level above a pump. This system may also benefit from the use of various back pressure controls and fluid entry and reversal mechanisms.
The injector of the present invention may also be combined with an improved beam pumping unit as described in U.S. Pat. No. 3,971,213. This integrated system uses power derived from the pressure of natural gas produced in the annulus in the previously described liquid reservoir. After pressure reduction at the surface, the produced gas may be routed into a flow line for sale. No waste or burning of produced gas is required, and instead a self-contained operation is achieved.
The techniques of the present invention minimize the production of gas which, in many applications, is wasted and flared. By providing a controlled back pressure relief in a gas lifted well, a gas lift system in a flowing well may be configured with double packers to create a chamber above the producing formation. A tubing regulator device controls the pressure of entrapped gas from the wellbore which is relieved into the chamber, which in turn provides a desired pressure differential across the formation and to the wellbore. Gas in the chamber may further act as a first lifting stage for slugs of liquid entering the tubing. Various modifications to this technique are more fully discussed below. The techniques of the present invention may also be used to increase productivity in horizontal wells, as discussed further below. The techniques of the present invention may thus be used to increase liquid hydrocarbon recovery by conserving and utilizing natural gas as a reservoir driving mechanism so that a gas cap pushes the liquid downward to a lower horizontal bore hole or lateral.
It is an object of the present invention to provide improved equipment and methods for recovering hydrocarbons from subterranean formations. More particularly, the present invention may function to retain a pressurized gas reservoir downhole and thereby improve recovery of liquid hydrocarbons, and may also be used to remove liquids which block the effective recovery of gaseous hydrocarbons. The improved method of producing hydrocarbons from a well serves to more efficiently retain and utilize the inherent energy of natural gas within the reservoir. A properly designed system according to the present invention may create a reservoir producing mechanism that minimizes production problems and recovers significantly greater volumes of liquid hydrocarbon reserves.
It is a feature of the present invention that the techniques described herein may be used for maintaining a downhole reservoir so that the liquid injector may operate independent of an artificial lift system for the well. The methods of the present invention may also utilize a liquid injector below an annular seal or packer between the tubing and casing to provide for and control the relief of wellbore gas pressure buildup above the liquid in the wellbore and thereby optimize reservoir inflow performance. The liquid injector may also be incorporated with a gas lift system to achieve a design with enhanced wellbore to reservoir pressure drawdown and inflow patterns. The techniques of the present invention may be used to enhance hydrocarbon recovery from highly deviated or horizontal wellbores, and may also be used in directional well drilling and completion techniques.
One feature of the present system is that the injector provides benefits from improved control by preventing formation gas production with the production of liquids. The injector incorporates an improved sand filter and may utilize a liquid reservoir above a packer, and optionally employs a shutoff valve located closer to the pump. The techniques of the present invention may be used to minimize and prevent gas locking in pumped wells, and also minimize the likelihood of gas blowout to surface by allowing the injector to act as a downhole gas shutoff device. The techniques of the present invention further result in improved lubrication for the polished rod to minimize leakage of hydrocarbons through the stuffing box. The present invention may be used to effectively de-water gas wells by removing liquids that prevent optimum gas production. In wells in which liquid hydrocarbons are produced, gas waste is minimized and conservation of gas enhances gas drive capabilities.
A significant feature of the present invention is the improved long-term productivity and increased recovery of hydrocarbon reserves of existing oilfields. In new fields, the systems of the present invention provide an effective completion option over existing technology. By retaining a high percentage of natural gas within the reservoir and producing the oil by gravity drainage, more oil is recovered.
An advantage of the present invention is that highly sophisticated equipment and techniques are not required to significantly improve the production of hydrocarbons. Another significant advantage of the invention is the relatively low cost of the equipment and operating techniques as described herein compared to the significant advantages realized by the well operator. Moreover, the useful life of other hydrocarbon production equipment, such as downhole positive displacement pumps and wellhead stuffing boxes, is improved by the system provided by this invention.
These and further objects, features, and advantages of this invention will become apparent from the following detailed description, wherein reference is made to the figures in the accompanying drawings.